Filter element with retractable guidewire tip

ABSTRACT

A medical guidewire assembly comprises a guidewire having a flexible tip. A medical device such as a collapsible filter for use as an embolic protection device is mounted on the guidewire. The filter is advanced through a body lumen with the guidewire tip extending distally. At a first location the filter is advanced relative to the tip to a location which is distally advanced from the first location. Placement of the filter in an optimal distal location is thereby achieved.

This application is a continuation of U.S. application Ser. No.09/986,060, filed Nov. 7, 2001 now abandoned, which is a continuation ofPCT/IE00/00057, filed May 8, 2000, and is a continuation-in-part of U.S.application Ser. No. 09/188,472, filed Nov. 9, 1998, now U.S. Pat. No.6,336,934, the contents of each of these applications are incorporatedherein by reference.

This invention relates to a filter element for a transcatheter embolicprotection device.

INTRODUCTION

The invention is particularly concerned with filter elements fortranscatheter embolic protection devices of the type described in ourWO-A-9923976. One type of such embolic filter essentially comprises afilter body mounted on an associated collapsible support frame which canbe collapsed against the guidewire by means of a catheter for deploymentof the filter through a patient's vascular system. Upon retraction ofthe catheter the support frame and filter body expand outwardly from theguidewire across a blood vessel within which the filter is positioned tofilter blood flowing through the blood vessel.

One problem with the filter device is that there is a guidewire tip onthe distal end which is required for guiding the filter into a desiredposition. The guidewire tip needs to be relatively long to provide asmooth tip transition. However, the guidewire distal tip may interferewith the optimal placement of the filter element.

The present invention is directed towards overcoming this problem.

STATEMENTS OF INVENTION

According to the invention there is provide a medical guidewire assemblycomprising:

-   -   guidewire having a flexible tip at a distal end of the        guidewire;    -   a medical device mounted near the distal end of the guidewire        proximally of the tip, the medical device being movable relative        to the tip for adjustment of the amount of the tip extending        distally of the medical device;    -   and means to limit the movement of the medical device relative        to the tip.

In a preferred embodiment of the invention the means to limit themovement of the medical device comprise one or more stiff limitingelements.

Preferably at least one limiting element is provided on the guidewire.The limiting element may be fixedly mounted to the guidewire.Alternatively, the limiting element is slidably mounted on theguidewire. In this case preferably the assembly includes stop means tolimit slidable movement of the limiting element relative to theguidewire. The stop means to limit slidable movement of the limitingelement preferably comprises a pair of stops spaced axially apart alongthe guidewire. The stops may be provided by abutment surfaces formed inthe guidewire.

In a preferred embodiment of the invention at least one limiting elementis mounted to the medical device. Preferably the limiting element ismounted to the medical device at the proximal end of the medical device.In one arrangement the limiting element is mounted intermediate proximaland distal ends of the medical device.

In one embodiment of the invention at least one limiting element isstiff relative to the guidewire.

Alternatively or additionally at least one limiting element is compliantrelative to the guidewire.

Preferably the medical device and the tip are slidable relative to eachother. Ideally, the medical device has a receiver slot for reception ofat least portion of the tip. In one embodiment of the invention the tipis fully retractable within the receiver slot.

In a particularly preferred embodiment of the invention the medicaldevice is a collapsible embolic filter mounted on a tubular sleeve whichis slidably mounted on the guidewire adjacent the distal end of theguidewire, the sleeve having a bore through which the guidewire passes,said bore forming a receiver slot for reception of the flexible tip ofthe guidewire which is at least partially retractable within the bore ofthe sleeve.

Preferably the tip is fully retractable within the bore of the sleeve.

In one embodiment a guidewire limiting element is mounted to theguidewire proximal of the embolic filter and a filter limiting elementis mounted to the filter within the bore of the sleeve, the guidewirebeing movable relative to the filter between the first and secondlimiting elements. In this case preferably the guidewire has an abutmentwhich is engagable with the filter limiting element when the guidewiretip is retracted. In one embodiment the abutment is provided by ashoulder of the tip.

In one arrangement the filter limiting element is provided at a proximalend of the filter.

In another arrangement the filter limiting element is providedintermediate proximal and distal ends of the filter.

In another embodiment of the invention a guidewire limiting element ismounted to the guidewire intermediate proximal and distal ends of thefilter and the filter has a proximal filter limiting element and adistal filter limiting element, the guidewire limiting element beingmovable with the guidewire between the proximal and distal filterlimiting elements.

In one case the guidewire tip is retractable proximally of the distalfilter limiting element.

Preferably the guidewire limiting element is movable on the guidewire.In this case the assembly includes stop means to limit slidable movementof the guidewire limiting element relative to the guidewire. The stopmeans may comprise a pair of stops spaced axially apart along theguidewire. The stops may be provided by abutment surfaces formed in theguidewire. In one embodiment the guidewire has a recessed portion ofreduced diameter on which the guidewire limiting element is mounted.

In another aspect the invention provides an embolic protection devicecomprising:

-   -   a collapsible filter element mounted on a filter carrier for        delivery through a vascular system of a patient;    -   the filter element being movable between a collapsed stored        position against the filter carrier for movement through the        vascular system, and an expanded position for occluding a blood        vessel such that blood passing through the blood vessel is        delivered through the filter element;    -   the filter element comprising a collapsible filter body having        an inlet end and an outlet end;    -   the inlet end of the filter body having one or more inlet        openings sized to allow blood and embolic material enter the        filter body;    -   the outlet end of the filter body having a plurality of outlet        openings sized to allow through passage of blood but to retain        undesired embolic material within the filter body;    -   the collapsible filter element being slidably mounted on the        filter carrier for axial movement of the filter element along        the filter carrier; and    -   means to limit the movement of the filter element relative to        the filter carrier, the means being arranged to allow a distal        end of the filter carrier to be substantially retracted into the        filter element.

In one embodiment of the invention the means to limit the movement ofthe filter element comprise one or more limiting elements.

At least one limiting element is preferably provided on the filtercarrier.

The limiting element may be fixedly mounted on the filter carrier.

Alternatively the limiting element is slidably mounted on the filtercarrier. In this case the device preferably includes stop means to limitthe movement of the limiting element relative to the filter carrier. Themeans to limit the movement of the limiting element may comprise a pairof stops spaced axially apart along the filter carrier. The stops may beprovided by abutment surfaces formed on the filter carrier.

In a preferred embodiment of the invention at least one limiting elementis mounted to the filter element. The limiting element may be mounted tothe filter element intermediate the proximal and distal ends of thefilter element.

In one embodiment of the invention at least one limiting element isstiff relative to the filter carrier. Alternatively or additionally atleast one limiting element is compliant relative to the filter carrier.

The limiting element may be mounted to the filter element at theproximal end of the filter element.

In a particularly preferred embodiment of the invention the filtercarrier is a guidewire. Preferably the distal end of the guidewireincludes a guiding tip which may be substantially retracted into thefilter element.

The invention also provides a method for positioning a medical device ina body lumen comprising the steps of:

-   -   providing a medical guidewire assembly of the invention;    -   advancing the assembly into a body lumen with the guidewire tip        extending distally of the medical device to a first location;    -   moving the medical device relative to the tip to advance the        medical device to a second location which is distally advanced        from the first location.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood by the followingdescription of some of the embodiments thereof, given by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 is partially sectioned elevational view of an embolic protectiondevice;

FIG. 2 is a schematic sectional elevational view of the embolicprotection device of FIG. 1;

FIG. 3 is a detail sectional view of a portion of the device of FIG. 1;

FIG. 4 is a longitudinal cross sectional view of the device of FIG. 1;

FIG. 5 is a cross sectional view of a distal end of the device of FIG.1;

FIG. 6 is a view on the line A-A in FIG. 4;

FIG. 7 is a perspective view of a filter body of the device of FIGS. 1to 6;

FIG. 8 is a side elevational view of the filter body of FIG. 7;

FIG. 9 is a view on a proximal end of the filter body;

FIG. 10 is a perspective view of a support frame of the device of FIGS.1 to 6;

FIG. 11 is a side elevational view of the support frame;

FIG. 12 is a perspective view illustrating the manufacture of thesupport frame;

FIG. 13 is a view of the support frame and filter body assembly;

FIG. 14 is a side partially cross sectional view of a filter body andguidewire according to one embodiment of the invention in one positionof use;

FIG. 15 is a side view similar to FIG. 14 in another position of use;

FIG. 16 is a side, partially cross sectional view of a filter body andguidewire according to another embodiment of the invention in oneposition of use;

FIG. 17 is a side view similar to FIG. 16 in another position of use;

FIG. 18 is a side partially cross sectional view of a filter body andguidewire according to a further embodiment of the invention in oneposition of use;

FIGS. 19 and 20 are side views similar to FIG. 18 in other positions ofuse; and

FIGS. 21 to 23 are side, partially cross sectional views of a filterbody and guidewire according to a further embodiment of the invention indifferent positions of use.

DETAILED DESCRIPTION

Referring to FIGS. 1 to 13 there is illustrated an embolic protectiondevice as described in our WO-A-9923976 indicated generally by thereference number 100. The device 100 has a guidewire 101 with a proximalend 102 and a distal end 103. A tubular sleeve 104 is slidably mountedon the guidewire 101. A collapsible filter 105 is mounted on the sleeve104, the filter 105 being movable between a collapsed stored positionagainst the sleeve 104 and an expanded position as shown in the drawingsextended outwardly of the sleeve 104 for deployment in a blood vessel.

The sleeve 104 is slidable on the guidewire 101 between a pair ofspaced-apart end stops, namely an inner stop 106 and an outer stop whichin this case is formed by a spring tip 107 at the distal end 103 of theguidewire 101.

The filter 105 comprises a filter body 110 mounted over a collapsiblesupport frame 111. The filter body 110 is mounted to the sleeve 104 ateach end, the body 110 being rigidly attached to a proximal end 112 ofthe sleeve 104 and the body 110 being attached to a collar 115 which isslidable along a distal end 114 of the sleeve 104. Thus the distal endof the body 110 is longitudinally slidable along the sleeve 104. Thesupport frame 111 is also fixed at the proximal end 112 of the sleeve104. A distal end 116 of the support frame 111 is not attached to thesleeve 104 and is thus also free to move longitudinally along the sleeve104 to facilitate collapsing the support frame 111 against the sleeve104. The support frame 111 is such that it is naturally expanded asshown in the drawings and can be collapsed inwardly against the sleeve104 for loading in a catheter 118 or the like.

The filter body 105 has large proximal inlet openings 117 and smalldistal outlet openings 119. The proximal inlet openings 117 allow bloodand embolic material to enter the filter body, while, the distal outletopenings 119 allow through passage of blood but retain undesired embolicmaterial within the filter body.

An olive guide 120 is mounted at a distal end of the sleeve 104 and hasa cylindrical central portion 121 with tapered ends 122, 123. The distalend 122 may be an arrowhead configuration for smooth transition betweenthe catheter and olive surfaces. The support frame 111 is shaped toprovide a circumferential groove 125 in the filter body 110. If thefilter is too large for a vessel, the body may crease and this groove125 ensures any crease does not propagate along the filter.

Enlarged openings are provided at a proximal end of the filter body 110to allow ingress of blood and embolic material into an interior of thebody 110.

In use, the filter 105 is mounted in a collapsed state within a distalend of the catheter 118 and delivered to a deployment site. When thefilter is correctly positioned the catheter 118 is retracted allowingthe support frame 111 to expand expanding the filter body 110 across thevessel in which the filter is mounted. Blood and emboli can enter theenlarged openings at a proximal end of the filter body 110. The bloodwill pass through the filter body, however, the openings or pores in thefilter body are sized so as to retain the embolic material. After use, aretrieval catheter 18 is delivered along the guidewire 101 and slid overthe filter 105 engaging the proximal inlet end 112 first to close theopenings and then gradually collapsing the filter body against thesleeve 104 as the catheter 118 advances over the filter 105. Once thefilter 105 is fully loaded in the catheter 118, it can then bewithdrawn.

It will be noted that a proximal end of the filter is fixed and a distalend of the filter is longitudinally movable along the sleeve tofacilitate collapsing of the filter body.

Further, the catheter engages the proximal end of the filter body firstthus closing the filter body inlet and preventing escape of embolicmaterial from the filter body as the filter body is being collapsed.

The outer filter body 110 is preferably of a resilient biocompatibleelastomeric material. The material may be a polyurethane based material.There are a series of commercially available polyurethane materials thatmay be suitable. These are typically based on polyether or polycarbonateor silicone macroglycols together with diisocyanate and a diol ordiamine or alkanolamine or water chain extender. Examples of these aredescribed in EP-A-461,375 and U.S. Pat. No. 5,621,065. In addition,polyurethane elastomers manufactured from polycarbonate polyols asdescribe U.S. Pat. No. 5,254,622 (Szycher) are also suitable.

The filter material may also be a biostable polycarbonate urethanearticle example of which may be prepared by reaction of an isocyanate, achain extend and a polycarbonate copolymer polyol of alkyl carbonates.This material described in our WO-A-9924084. The filter material may bemanufactured from a block and cut into a desired shape. However thefilter is preferably formed by dipping a rod of desired geometry into asolution of the material which coats the rod. The rod is then dissolved.The final geometry of the filter may be determined in the dipping stepor the final geometry may be achieved in a finishing operation.Typically the finishing operations involve processes such as mechanicalmachining operations, laser machining or chemical machining.

The filter body is of hollow construction and is formed as describedabove by dipping a rod in a solution of polymeric material to coat therod. The rod is then dissolved, leaving a hollow body polymericmaterial. The rod may be of an acrylic material which is dissolved by asuitable solvent such as acetone.

The polymeric body thus formed is machined to the shape illustrated inFIGS. 1 to 13. The final machined filter body comprises an inlet orproximal portion 210 with a proximal neck 212, and outlet or distalportion 213 with a distal neck 214, and an intermediate portion 215between the proximal and distal portions.

The inlet holes 117 are provided in the proximal portion 210 which allowthe blood and embolic material to flow into the filter body. In thiscase the proximal portion 210 is of generally conical shape to maximisethe hole size.

The intermediate portion 215 is also hollow and in this case is ofgenerally cylindrical construction. This is important in ensuring morethan simple point contact with the surrounding blood vessel. Thecylindrical structure allows the filter body to come into soft contactwith the blood vessel to avoid damaging the vessel wall.

The intermediate portion 215 is provided with a radial stiffening means,in this case in the form of a radial strengthening ring or rim 220. Thering 220 provides localised stiffening of the filter body withoutstiffening the material in contact with the vessel. Such an arrangementprovides appropriate structural strength so that line apposition of thefilter body to the vessel wall is achieved. It is expected that othergeometries of stiffening means will achieve a similar result.

The tubular intermediate portion 215 is also important in maintainingthe stability of the filter body in situ to retain captured emboli andto ensure that flow around the filter is minimised. For optimumstability we have found that the ratio of the axial length of theintermediate portion 215 of the filter body to the diameter of theintermediate portion 215 is preferably at least 0.5 and ideally greaterthan 1.0.

The collapsible support frame 111 has four foldable arms 290 which arecollapsed for deployment and upon release extend outwardly to expand thefilter body 110.

The support frame 111 can be manufactured from a range of metallic orpolymeric components such as a shape memory alloy like nitinol or ashape memory polymer or a shaped stainless steel or metal with similarproperties that will recover from the deformation sufficiently toinitiate opening of the filter body 110.

The support frame may be formed as illustrated in FIG. 12 by machiningslots in a tube 291 of shape memory alloy such as nitinol. On machining,the unslotted distal end of the tube forms a distal collar 293 and theunslotted proximal end of the tube forms a proximal collar 294. In use,the distal collar 293 is slidably moveable along the tubular sleeve 104which in turn is slidably mounted on the guidewire 101 for deploymentand retrieval. The proximal collar 294 is fixed relative to the tubularsleeve 104.

To load the filter the sub assembly of the support frame and filter bodyis pulled back into the catheter 118 to engage the distal stop 107. Thesupport arms 290 are hinged inwardly and the distal collar 293 movesforward along the tubular sleeve 104. As the support arms 290 enter thecatheter 118 the filter body 110 stretches as the filter body collar 115slides along the tubular sleeve 104 proximal to the olive 120. Ondeployment, the catheter 118 is retracted proximally along the guidewire101 initially bringing the collapsed filter assembly with it until itengages the proximal stop 106. The catheter sleeve then begins to pulloff the filter, freeing the support arms 290 to initiate opening of thefilter body to appose the vessel wall.

For retrieval, a retrieval catheter is introduced by sliding it over theguidewire 101 until it is positioned at the proximal end of the filterbody and support frame. Pulling the guidewire 101 will initially engagethe distal stop 107 with the filter element and begin to pull it intothe retrieval catheter. The initial travel into the delivery catheteracts to close the proximal openings of the filter element, thusentrapping the embolic load. As the filter continues to be pulled backthe filter body and the support frame are enveloped in the retrievalcatheter. The collapsed filter may then be removed from the patient.

Referring to FIGS. 14 and 15 there is illustrated a medical guidewireassembly according to one embodiment of the invention. A filter 31 ismounted on a guidewire 30 and projecting from the distal end of theguidewire 30 is a guidewire tip 32. The guidewire tip 32 is slidable ina bore 38 in a sleeve 39 of the filter 31. When the filter 31 is beingmanoeuvred into place the guidewire tip 32 facilitates the manoeuvringof the filter device. By advancing and retracting the tip 32 relative tothe filter assembly 31 it is possible to manoeuvre the guidewire tip 32around various portions of the anatomy, for example, where it isparticularly tortuous, or where the guidewire tip 32 has to crosslesions. The tip 32 can be partially retracted to give a stiffer tip, orcan be fully retracted in the deployment position, FIG. 15.

The guidewire 30 is slidable between a proximal guidewire limitingelement 35 on the guidewire 30 and a filter limiting element 37 providedat a proximal end of the filter 31. A stop defined by a shoulder 36 ofthe tip 32 is engagable against the limiting element 37.

The proximal limiting element 35 and the filter limiting element 37 areof a relatively stiff material, such that upon engagement of the filter31 with the proximal limiting element 35, or the shoulder 36 with thefilter limiting element 37, the limiting elements 35, 37 do not deform.In this way the movement of the filter 31 relative to the guidewire tip32 is accurately controlled.

One or both of the limiting elements 35, 37 may be of a compliantmaterial. This feature will assist in ensuring that the flexibility ofthe filter is not affected by the limiting elements.

Referring to FIGS. 16 and 17 there is illustrated a medical guidewireassembly including a filter 42, which is similar to the filter 31 ofFIGS. 14 and 15, and the same reference numerals are used to denotesimilar elements in FIGS. 16 and 17. In this case the guidewire 30 isslidable between a proximal limiting element 35 on the guidewire 30 anda filter limiting element 40 positioned intermediate the proximal anddistal ends of the filter 42. A distal stop defined by a shoulder 36 ofthe tip 32 is engagable against the filter limiting element 40.

Referring to FIGS. 18 to 20 there is illustrated a medical guidewireassembly including a filter 50, which is similar to filters 31 and 42 ofFIGS. 14 to 17, and the same reference numerals are used to denotesimilar elements in FIGS. 18 to 20. In this arrangement a guidewirelimiting element 51 is rigidly fixed to the guidewire 30 proximal of thetip 32, the filter 50 being mounted on the guidewire 30 so that thelimiting element 51 is intermediate the proximal and distal ends of thefilter 50. The guidewire 30 is slidable between a distal limitingelement defined by a proximal shoulder 53 of the filter 50 which isengagable against the guidewire limiting element 51, and a proximallimiting element defined by a distal shoulder 52 of the filter 50 whichis engagable against the guidewire limiting element 51. In thisarrangement there is no obstruction to advancement of another medicaldevice over the guidewire 30 to approach the filter 50 from the proximaldirection.

Referring to FIGS. 21 to 23 in an alternative embodiment of theinvention, the guidewire limiting element 51 is slidably mounted withina recess 53 provided on the guidewire 30, the movement of the limitingelement 51 relative to the guidewire 30 being limited between a proximalstop provided by a shoulder 55 of the recess and a distal stop providedby a shoulder 54 provided by the guidewire tip 32. This arrangementprovides an even greater degree of freedom for movement of the guidewire30 relative to the filter.

The filter may be placed over or beyond the distal guidewire tip. Thus,the invention facilitates the optimal placement of a filter device inthe limited vasculature space available.

Other medical devices may be advanced over the guidewire to approach thefilter from the proximal direction without obstruction. Such devices maybe for use in performing angioplasty procedures, stenting and the like.Ready access is also provided to perform emergency procedures such assnaring of a medical device or part, and lysis for treatment of a bloodclot.

It will be appreciated that while the invention has been described inrelation to an embolic protection device it may also be applied tomedial guidewire assemblies for placement of other medical devices.

The invention is not limited to the embodiments hereinbefore describedwhich may be varied in both construction and detail.

1. A medical guidewire assembly comprising: a guidewire having aflexible tip at a distal end of the guidewire; an expandable medicaldevice having a collapsed and expanded configuration mounted near thedistal end of the guidewire proximally of the tip, the medical devicebeing in its collapsed and expanded configurations movable relative tothe tip for adjustment of the amount of the tip extending distally ofthe medical device; and means to limit the movement of the medicaldevice relative to the tip.
 2. A medical guidewire assembly as claimedin claim 1 wherein the means to limit the movement of the medical devicecomprise one or more stiff limiting elements.
 3. A medical guidewireassembly as claimed in claim 2 wherein at least one limiting element isprovided on the guidewire.
 4. A medical guidewire assembly as claimed inclaim 3 wherein the limiting element is fixedly mounted to theguidewire.
 5. A medical guidewire assembly as claimed in claim 3 whereinthe limiting element is slidably mounted on the guidewire.
 6. A medicalguidewire assembly as claimed in claim 5 including stop means to limitslidable movement of the limiting element relative to the guidewire. 7.A medical guidewire assembly as claimed in claim 6 wherein the stopmeans to limit slidable movement of the limiting element comprises apair of stops spaced axially apart along the guidewire.
 8. A medicalguidewire assembly as claimed in claim 7 wherein the stops are providedby abutment surfaces formed in the guidewire.
 9. A medical guidewireassembly as claimed in claim 2, wherein at least one limiting element ismounted to the medical device.
 10. A medical guidewire assembly asclaimed in claim 9 wherein the limiting element is mounted to themedical device at the proximal end of the medical device.
 11. A medicalguidewire assembly as claimed in claim 10, wherein the limiting elementis mounted intermediate proximal and distal ends of the medical device.12. A medical guidewire assembly as claimed in claim 2, wherein at leastone limiting element is stiff relative to the guidewire.
 13. A medicalguidewire assembly as claimed in claim 1, wherein the medical device andthe tip are slidable relative to each other.
 14. A medical guidewireassembly as claimed in claim 1, wherein the medical device has areceiver slot for reception of at least portion of the tip.
 15. Amedical guidewire assembly as claimed in claim 14 wherein the tip isfully retractable within the receiver slot.
 16. A medical guidewireassembly as claimed in claim 1, wherein the medical device is acollapsible embolic filter mounted on a tubular sleeve which is slidablymounted on the guidewire adjacent the distal end of the guidewire, thesleeve having a bore through which the guidewire passes, said boreforming a receiver slot for reception of the flexible tip of theguidewire which is at least partially retractable within the bore of thesleeve.
 17. A medical guidewire assembly as claimed in claim 16 whereinthe tip is fully retractable within the bore of the sleeve.
 18. Amedical guidewire assembly as claimed in claim 16 wherein a guidewirelimiting element is mounted to the guidewire proximal of the embolicfilter and a filter limiting element is mounted to the filter within thebore of the sleeve, the guidewire being movable relative to the filterbetween the first and second limiting elements.
 19. A medical guidewireassembly as claimed in claim 18 wherein the guidewire has an abutmentwhich is engagable with the filter limiting element when the guidewiretip is retracted.
 20. A medical guidewire assembly as claimed in claim19 wherein the abutment is provided by a shoulder of the tip.
 21. Amedical guidewire assembly as claimed in claim 18, wherein the filterlimiting element is provided at a proximal end of the filter.
 22. Amedical guidewire assembly as claimed in claim 18, wherein the filterlimiting element is provided intermediate proximal and distal ends ofthe filter.
 23. A medical guidewire assembly as claimed in claim 16wherein a guidewire limiting element is mounted to the guidewireintermediate proximal and distal ends of the filter and the filter has aproximal filter limiting element and a distal filter limiting element,the guidewire limiting element being movable with the guidewire betweenthe proximal and distal filter limiting elements.
 24. A medicalguidewire assembly as claimed in claim 23 wherein the guidewire tip isretractable proximally of the distal filter limiting element.
 25. Amedical guidewire assembly as claimed in claim 23 wherein the guidewirelimiting element is movable on the guidewire.
 26. A medical guidewireassembly as claimed in claim 25 including stop means to limit slidablemovement of the guidewire limiting element relative to the guidewire.27. A medical guidewire assembly as claimed in claim 26 wherein the stopmeans comprises a pair of stops spaced axially apart along theguidewire.
 28. A medical guidewire assembly as claimed in claim 27wherein the stops are provided by abutment surfaces formed in theguidewire.
 29. A medical guidewire assembly as claimed in claim 26,wherein the guidewire has a recessed portion of reduced diameter onwhich the guidewire limiting element is mounted.
 30. A method forpositioning a medical device in a body lumen comprising the steps of:providing a medical guidewire assembly as claimed in claim 1; advancingthe assembly into a body lumen with the guidewire tip extending distallyof the medical device to a first location; moving the medical devicerelative to the tip to advance the medical device to a second locationwhich is distally advanced from the first location.
 31. An embolicprotection device comprising: a collapsible filter element mounted on afilter carrier for delivery through a vascular system of a patient; thefilter element being movable between a collapsed stored position againstthe filter carrier for movement through the vascular system, and anexpanded position for occluding a blood vessel such that blood passingthrough the blood vessel is delivered through the filter element; thefilter element comprising a collapsible filter body having an inlet endand an outlet end; the inlet end of the filter body having one or moreinlet openings sized to allow blood and embolic material enter thefilter body; the outlet end of the filter body having a plurality ofoutlet openings sized to allow through passage of blood but to retainundesired embolic material within the filter body; the collapsiblefilter element being slidably mounted on the filter carrier for axialmovement of the filter element in its collapsed and expandedconfigurations along the filter carrier; and means to limit the movementof the filter element relative to the filter carrier, the means beingarranged to allow a distal end of the filter carrier to be substantiallyretracted into the filter element.
 32. An embolic protection device asclaimed in claim 31 wherein the means to limit the movement of thefilter element comprise one or more limiting elements.
 33. An embolicprotection device as claimed in claim 31 wherein at least one limitingelement is provided on the filter carrier.
 34. An embolic protectiondevice as claimed in claim 33 wherein the limiting element is slidablymounted on the filter carrier.
 35. An embolic protection device asclaimed in claim 33 wherein the limiting element is fixedly mounted onthe filter carrier.
 36. An embolic protection device as claimed in claim35 including stop means to limit the movement of the limiting elementrelative to the filter carrier.
 37. An embolic protection device asclaimed in claim 36 wherein the means to limit the movement of thelimiting element comprises a pair of stops spaced axially apart alongthe filter carrier.
 38. An embolic protection device as claimed in claim37 wherein the stops are provided by abutment surfaces formed on thefilter carrier.
 39. An embolic protection device as claimed in claim 31,wherein at least one limiting element is mounted to the filter element.40. An embolic protection device as claimed in claim 39 wherein thelimiting element is mounted to the filter element intermediate theproximal and distal ends of the filter element.
 41. An embolicprotection device as claimed in claim 31, wherein at least one limitingelement is stiff relative to the filter carrier.
 42. An embolicprotection device as claimed in claim 39 wherein the limiting element ismounted to the filter element at the proximal end of the filter element.43. An embolic protection device as claimed in claim 31, wherein thefilter carrier is a guidewire.